On a 2006 or 335i, I would change it preventively. The water pump design was changed IIRC. Also heat seems to be a contributing factor in the case of the 335i.
I wouldn't do it on a 2007+ N52. I hope not to regret it! I check monthly my codes...
2007 E90 AW 323i Step | Lowered 1.25"/1" | BMW Performance Exhaust | Debadged | Scangauge II | Style 162 18" & 161 17" wheels & rear 15mm spacers